Thermostatic apparatus



1931- w. B. HODGE 1,819,987

THERMOSTATIG APPARATUS Filed April 25, 1929 Fig. 2,

IQ'III III I I I I I I II I William B. Hodge ymwkw Afiys.

Patented Aug. 18, 1931 UNITED STATES PATENT OFFICE WILLIAM B. HODGE, OF CHARLOTTE, NORTH CAROLINA, ASSIGNOR TO PARKS-CRAMER COMPANY, OF FITCHBUBG, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS THERMOSTATIC APPARATUS Application filed April 23,

This invention relates to improvements in thermo-sensitive elements of the type commonly known in the art as capsule elements, or diaphragm motors, suitable for the actuation of thermostatic apparatus.

Such elements are usually of annular form and consist of two walls of flexible metal rigidly attached together and hermetically sealed at their periphery. The diaphragm walls are usually composed of thin metal sheets having means such as annular grooves or corrugations which are intended to increase the flexibility of the diaphragms so as to permit the greatest possible distortion by the pressure of the expansible fluid contained within the walls of the element. 7

Such elements are usually charged with a limited quantity of any suitable volatile fluid. The diaphragm walls are, therefore, subject to the vapor pressure characteristic of the fluid at the temperature to which the element is exposed. As the temperature varies, the vapor pressure changes in accordance with the characteristics of the fluid and the resulting distortion of the walls is utilized to actuate suitable mechanism for indicating or registering the temperature of an enclosure, or for initiating the action of mechanism operable to control the temperature .or the condition of humidity of the enclosure, or both.

It is characteristic of those volatile fluids which are commonly used for such purposes that as the temperature is increased, the pressure of the vapor increases not in direct/proportion to changes in temperature, but at a rate which progressively increases.

- The ordinary diaphragms commonly used for such purposes are provided with annular corrugations for the purpose of increasing their range of axial distortion in response to changes in temperature. Since the vapor pressure of the volatile fluids in common use increases in rapid progression with respect to uniform increments of increase in temperature, there is in consequence a similar and considerable increase in the rate of axial distortion with respect to temperature, so that equal increments of increase in temperature are reflected in progressively increasing incre- 1929. Serial No. 357,460.

ments of distortion in the performance of ordinary diaphragms of this type.

Where such thermo-sensitive elements are used in instruments for indicating and recording temperatures, or for actuating mechanism to control temperature or the humidity of an enclosure, this progressivelyincreasing expansion of the thermo-sensitive element is decidedly disadvantageous, and numerous attempts have been made to reduce or eliminate it by the application of compensating devices, such as a spring so disposed with reference to the diaphragm as to subject it to progressively increasing resistance, or by the provision of devices for translating the variable movements of the diaphragm, caused by uniform changes in temperature, into uniform movements. Such attempts have necessarily introduced many mechanical complications resulting in costly constructions which easily get out of order and at best only produce approximately uniform movements correlated to uniform changes in temperature.

The principal object of the present invention is to produce a thermo-sensitive element of the well-known diaphragm-motor type,

whose axial expansion in response to increas ing temperature shall be characterized by uniform increments of expansion in response to uniform increments of temperature-that is to say, a diaphragm motor possessing a uniform coeflicient of expansion throughout a predetermined. temperature range.

In the present type of my invention, this is accomplished by making use of an element comprising a closed recepticle for a volatile fluid having an elastic annular diaphragm wall or walls, of spherical form, subject to thevapor pressure of the fluid within, and

operable to oppose progressively increasing increments of resistance to axial distortion .of said wall or walls, the said resistance being so correlated to the progressive rate of i crease in the increments of vapor pressure produced by uniform increments of temperature as to compensate for said progressive increase in pressure. I have discovered that a thermo-sensitive 'elementpr cell with a confined volatile fluid and having oppositely disposed like diaplaying altered characteristics phragm walls of thin sheet metal peripherally united and re-enforced to provide a rigid annulus, with the effective areas of the walls circumscribed by said annulus expansible spherically within a predetermined range, and having such resilience as to offer progressively varying resistance to spherical expansion by the vapor pressure of the fluid in direct proportion to and compensatory of varying increments of vapor pressure produced by such uniform increments of temperature, will result in uniform increments of axial movement of the respective diaphragms in response to uniform increments of temperature.

I have also discovered that a thermo-sensitive element or cell confining a volatile fluid and having oppositely disposed like diaphragm walls of thin sheet metal peripherally united to provide a rigid annulus, with the effective areas of said walls circumscribed by said annulus, initially flat, but spherically distorted by the vapor pressure of the fluid, behaves in accordance with a law which causes it to function in the desired manner above described.

Diaphragms of the preferred type herein disclosed and described are embodiments of these novel discoveries and do in fact function in the desired manner. When subjected to uniform increments of temperature they respond with uniform increments of axial distortion and may, therefore, be properly described as having a uniform coeflicient of axial expansion with respect to tempera ture.

So long as the temperature is not sufliciently high to produce pressures that will strain the material, of which the diaphragm is composed, beyond its elastic limit, the element or cell will return to its initial condition as temperature is reduced and will repeat its performance indefinitely without dis set. The effective range of temperature for such an element is bounded by the boiling point of the fluid used on the one hand, and on the other by the temperature at which the resultant vapor pressure produces a strain in the material of the diaphragm that approaches its elastic limit.

Diaphragms of the usual type with annular corrugations are commonly manufactured by the well-known process of spinning,

.and have been found to be characterized by great variation in uniformity, which is due to variable pressure of the spinning tool and.

variations in the fiow? of the metal, as a result of said pressure.

Such diaphragms, therefore, are seldom or never interchangeable, because of their variable characteristics, and when assembling .them into actuating elements for thermostatic instruments, careful calibration and selection is necessary, so that the production or permanent of units whose characteristics are suitable for their purposes is a necessarily expensive process.

Another object of the invention is to provide a diaphragm adaptable to inexpensive production by pressing, in preference to the more expensive and less easily controlled method known as spinning, with the purpose of attaining both economy of production and improved uniformity and interchangeability in the product, it being highly desirable that the diaphragm motors as finally produced shall have strictly uniform characteristics of expansion and that any group assembly of such diaphragm units shall have the same rate of expansion and the same total expansion within and throughout-a given range of temperature as any other group-assembly of like units of the same number.

One important advantage of the present invention is the absence of localized strains in the diaphragm surfaces-a condition tending to increase the life of the diaphragm motor units under their ordinary duty. Corrugated diaphragms are necessarily subject to localized annular stresses and strains between the corrugations, and such diaphragms frequently fail under duty, as the result of crystallization and cracking of the metal on the lines where such strains occur.

The diaphragms having the smooth spherical surface of my improved type, being free from such localized strains, show a greatly increased life when tested to destruction by alternating application and release of pressure.

I am aware that heretofore use has been madein the thermostatic art of actuating elements, such as barsof expansible material, which have uniform coeflicient of expansion, but the expansive movements of such elements in the usual ranges of temperature to which the same are subjected are practically microscopic and are diflicult to utilize mechanically in thermostatic indicating, recording and regulating, instruments.

By the present invention fluid-actuated thermo-sensitive elements are provided which have a uniform coefficient of expansion throughout the usual temperature range to which such elements are subjected and which produce very considerable and measurable axial movements which can be readily utilized to actuate the indicating, recording or regulating mechanisms of the instruments in which they are employed.

These and other objects and features of the invention will more fully appear from the following description and the accompanying drawings and will be particularly pointed out in the claims.

In the drawings:

Fig. 1 is a vertical sectional view of a Simple form of thermo-sensitive element emof' the valve illustrated in Fig. 5, through Fig. 2 is a plan view of the same;

Fig. 3 is a view in vertical diametrical section showing in superposed relation the members of a thermo-sensitive element having oppositely disposed diaphragm walls. and illustrating also the manner in which the same are assembled;

Fig. i is a vertical diametrical sectional view of a preferred form of thermo-sensitive element embodying the present invention;

Fig. 5 is a view, mainly in vertical section, illustrating groups or batteries of thermosensitive elements embodying the present invention as employed in a regulating instrument operable by the wet and dry bulb temperatures of the air, and also showing the manner in which the regulatorcontrols the supply-of humidity of a typical moisturesupplying mechanism; and,

Fig. 6 is a detail view, partly in section,

which the action of the regulator operates to control the supply of'humidity to an enclosure.

Ordinary temperatures of factories, work shops, schools, dwellings, etc., in which temperature indicating, recording and regulating instruments are used, or in which humidity regulating devices are employed, range from approximately fifty-five degrees to one hundred and ten degrees, Fahrenheit.

The predetermined temperature range within which the vapor of a volatile fluid may be utilized to actuate a thermostatic element of the diaphragm or capsule type is limited by practical considerations, as is well lmown in the art.

The upper limit of temperature must be lower than any temperature which would generate pressures sufficient to strain the maierial of the diaphragms beyond its elestic imit.

:lliggtly higher than the boiling point of the These considerations apply with equal force to diaphragms of the corrugated type and also to diaphragms of my improved type. An important advantage which diaphragms of my improved type derive from my inven tion is that within a predetermined temperature range, limited as above described, they have a uniform rate of axial expansion as temperature increases, as will presently be shown.

In the case of any volatile fluid confined in contact with its vapor at temperatures which exceed its boiling point, the relation between vapor pressure and temperature is such that the pressure exerted by the vapor increases progressively with increases in temperature.

That is. to say, there is a progressive in crease in the value of the increments in pressure produced by uniform increments of temperature. Reference t the Smithsonian The lower limit of temperature must be Physical Tables will show for instance that ethyl chloride, a volatile fluid frequentlyused as the expansive medium in such thermo-sensitive elements, has at a temperature of degrees C. a vapor pressure of 99.62 centimeters of mercury; at degrees C., a vapor pressure of 118.42; at.30 degrees C., a vapor pressure of 139.90; at 35 degrees C., a vapor pressure of 164.32; and at 40 degrees (3., 191.96.

'A temperature increase of five degrees C. from 20 degrees to 25 degrees shows an increase in vapor pressure of 18.80; a'five de" gree increase in temperature from 25 degrees to degrees shows an increase in vapor pressure of 21.48; a five degree increase in temperature from 30 degrees to'35 degrees shows an increase in vapor pressure of 24.42; and a five degree increase in temperature from degrees to 40 degrees shows an increase in vapor pressure of 27.61.

here a corrugated diaphragm is employed the flexibility of the diaphragm is such that the axial movement of the diaphragm produced by the progressively increasing vapor pressure is approximately proportional to the increase in vapor pressure.

If the elastic resistance to distortion of the diaphragm walls be constant or nearly so, as in the case of ordinary corrugated diaphragms, it is clear that the axial distortions due to equal increments of tempera- I ture will reflect the progressive increase in vapor pressure increments by a similar progressive increase in increments of distortion, which is, in fact, true, as is well-known in the art.

One of the distinctive characteristics of my present invention is the peculiar property possessed by elastic diaphragms with smooth. spherical surfaces of my improved type, which, as I have discovered, oppose a ro ressivelv increasin resistance to distortion in response to increasing vapor pressure, the rate of increase in resistance being so correlated to the rate of increase in pressure as to compensate therefor, and thereby produce uniform increments of axial distortion in response to uniform increments of temperature.

By virtue of this distinguishing characteristic, diaphragm motors of my improved type therefore become possessed of a uniform co-. eflicient of expansion throughout the predetermined range of temperature for which they are adapted.

I have also discovered that a diaphragm of my improved type is equally effective for the purposes of my invention whether it has an initially spherical surface of slight curvature, or whether it be initially flat, since the surface of a flat diaphragm is distorted into a spherical form as soon as any sensible pressure is-imposed upon it, and continues in a spherical form, the curvature of the sphere increasing and the radius decreasing as the pressure is increased.

The ability to use initially flat diaphragms is another advantageous feature of my invention, since manufacture may be accomplished more conveniently and cheaply than when initially corrugated or curved surfaces are required.

In manufacturing units of this type, th volatile fluid is commonly cooled to freezing temperatures by the influence of a mixture of ice and salt, or some other suitable freezing mixture, and is then introduced into the diaphragm elements which are subsequently sealed. Upon being subsequently exposed to higher temperatures than the boiling point of the fluid, vapor pressure as soon as generated will effect the initial distortion, which produces the desired spherical condition of the diaphragm surface.

I have found that sheet metals of the stronger and more elastic alloys, such as Phosphor bronze, are obtainable with such uniform thickness and elastic properties that diaphragm elements of my improved type manufactured from such material, when actuated by the vapor of ethyl chloride will consistently show an excellent performance characterized by all of the advantages above described.

Discs cut or pressed from high-grade sheet metal for manufacturing this improved type of diaphragm have proved to be so uniform that the completed diaphragms have uniform characteristics and to be interchangeable.

In the assembled groups of units, any assembly containing a given number of diaphragm elements is found to have the same uniform rate of expansion and the same total expansion within usual ranges of temperature as any other assembly of the same number of units.

The advantage of uniformity and interchangeability in such units and the absence of all necessity for calibration and'selection in assembling is an obvious advantage and results in great economy in manufacture.

A simple form ofapparatus is illustrated in Fig. 1 of the drawings which comprises a receptacle having a bottom or base 1 of preferably cylindrical form having an up-turned rigid peripheral flange 2 providing a chamber 3 for a volatile fluid, such as ethyl chloride. The receptacle is hermetically closed by a dia hragm 4, preferably of circular form and of a diameter equal to the diameter of the base 1. It may be rigidlv secured at its periphery to the flange 2 in any suitable mannor, as for example by soldering, and the periphery thereof, which overlies the flange 2 re-enforced by a rigid ring 5 soldered to the periphery of the disk, and'if desired also fixedly secured to the flange 2 by clamping screws, or otherwise.

.jected.

either case a suitable amount of volatile fluid is introduced into the receptacle at a temperature below the lower limit of the range of temperature to which the element is to be sub- In Figs. 3 and 4 a preferred'embodiment of the invention is illustrated which comprises a closed receptacle for a volatile fluid having oppositely disposed diaphragm walls. In this construction the diaphragm walls are of suitable elastic material, such as sheet bronze, and desirably are pressed to provide a flat effective area SllbJGOt to the vapor pressure of the fluid, and an olfset peripheral flange adapted when two of such diaphragms are superimposed in reverse relation to provide a chamber for the volatile fluid ,between the diaphragms.

As illustrated in Fig. 3 the lower diaphragm has a circular flat central portion 6 with a continuous, slightly ofl'set peripheral portion 7 and an upwardly bent annular flange or rim 8. The upper diaphragm has a central flat circular portion 9 with an integral offset peripheral portion 10 complementary to the oflset portion 7 of the lower diaphragm, but of slightly smaller diameter and adapted to seat within the peripheral flange 8 of thelower diaphragm.

In assembling the diaphragms together the peripheral portions 10 and 7 desirably are hermetically secured together by solder 11 and the flange 8 thereupon bent down upon the upper face of the peripheral portion 10 of the upper diaphragm and soldered thereto, thereby providinga soldered lock-seam joint. Desirably a rigid re-enforcing ring 12 is provided which has a horizontal flange 13 and a vertical flange 14, the vertical flange 14 being of such diameter as to fit upon the flange 8 of the lower diaphragm when its edge has been bent about the periphery of the upper diaphragm as above described, thereby providing a rigid annular peripheral support for the diaphragm which is effectively resistant to radial contraction or expansion in response to variations in the tension imposed upon the ring by the diaphragms due to the expansion and contraction of the vapor of a volatile fluid when subjected to different temperatures. The horizontal flange 14 is thereupon bent around and clamped upon the periphery 7 of the lower diaphragm, as illustrated in Fig. 4. The ring 12 desirably is also soldered to the peripheral portions and flanges of both diaphragms. The soldering together of the parts above described may be conveniently accomplished by tinning suflicient area of one or both of the contacting parts, so that when such parts are heated and pressure applied thereto the tin will melt and form the soldered joint. The diaphragms thus assembled are peripherally united to provide a rigid annulus circumscribing circular eflective areas which are expansible spherically within a predetermined range and produce uniform amounts of axial movement by elastic resistance compensatory of the varying amounts of vapor pressure of the confined fluid which result from uniform amounts of temperature variation.

The central portions of the diaphragms desirably are provided with rigid circular members of relatively smaller diameter by which the axial movements of the diaphragms may be transmitted to the usual indicating, recording or regulating mechanisms. Desira-bly the rigid central members are in the form of couplings by which the elements may be mounted or assembled in groups.

In the construction illustrated in Fig. 4 the expansible portion 6 of the lower diaphragm has secured centrally to it a cup-shaped coupling member 15 having a tubular stud 16 which extends through the central aperture in the member 6. A washer 17 fits around the stud 16 and the edge 18 of the stud is spun tightly down upon it, thereby clamping the coupling member 15 firmly to the diaphragm. The cup-shaped coupling member 15 is provided with internal screw threads 19 adapted to fit complementary external screw threads upon the coupling member which is secured to the opposite or upper diaphragm.

.ing the coupling firmly to the upper diaphragm.

Hermetic sealing of the parts of the coupling members to the diaphragms may be insured by soldering them together in the manner above described. I

The coupling member 20 of the upper diaphragm desirably is provided with a central aperture 25 having a screw threaded wall adapted to permit the introduction of volatile material into the chamber 26 of the element and which thereafter may be filled with a screw threaded plug, (not shown), and her- The uniform radial or axial movement of the diaphragm of a thermo-sensitive element, such as above described, embodying my invention, which is proportional to uniform changes in temperature is advantageous even inv the construction of a simple thermostat, since the dials with which all such thermostats are equipped can be calibrated in uniform graduations and the adjusting mechanism of each thermostat set so that any in strument will fit the standard dial.

A greater advantage, however, is derived from the use of thermo-sensitive elements embodying the invention in differential thermostats which are more familiarly known as wet and dry bulbhygrometers widely used for automatic control of the condition of humidity of the air of an enclosure.

A typical instrument of this class is illustrated in Fig. 5 together with the means operable thereby for regulating the amount of moisture delivered to the enclosure.

As illustrated in Fig. 5 the instrument comprises a casing 27, preferably of rectangular form, having a horizontal partition 28 a short distance from its upper end and a vertical partition 29 dividing the lower portion into a dry bulb chamber 30 and a wet bulb chamber 31 of approximately equal size. Air is permitted to enter the dry bulb chamber through a screened opening 32 in the bottom thereof and the partition 29 is provided with an aperture 33 through which the air may pass from the (11X bulb chamber to the wet bulb chamber. n opening 34 in the lower portion of one of the side walls of the wet bulb chamber permits the escape of the air from the wet bulb chamber. A spray head or atomizer 35 .is provided in the upper compartment 36 of the instrument and projects the spraydownwardly into the wet bulb compartment 31, thereby causing the circulation of a sample of the air of the enclosure, in which the instrument is located, upwardly through the dry bulb chamber, thence downwardly through the wet bulb chamber in which it is saturated and reduced to thepsychrometric temperature thereof.

Similiar groups or batteries of thermosensitive elements are provided in each of these chambers. As illustrated, the wet bulb member comprises four thermo-sensitive elements 37 of the character illustrated in Fig. 4, the exposed coupling member 38 of one of the outside members being mounted upon the stem of an adjusting screw 39 which has a screw threaded portion engaging the wall of the casing. The exposed coupling 40 of the outside thermo-sensitive member is pivotally connected to the lower arm 41 of a lever 42 which is pivotally mounted upon a bracket 43 of the casing. The upper end of the arm 42 extends through a suitable aperture in the partition 28 of the casing into the upper chamber 36 thereof. The lower end of the arm 41 of the lever is connected by a spring 44 to an arm 45 which is mounted upon the adjusting screw 39 and serves to hold the lower end of the lever arm in contact with the thermo-sensitive members during the contractive movements thereof.

The dry bulb thermostatic member of the .instrument is similarly constructed and comprises a battery 46 of four thermo-sensitive elements, the coupling member 47 of one of the outer elements being mounted upon a stud 48 extending from the partition wall 29 and the coupling member 49 of the other outside element being pivotally connected to the lower arm 50 of a lever which is fulcrumed upon a bracket 51 upon the casing. The upper arm 52 of the lever extends through a suitable aperture in the casing 28 and is provided at its upper end with a shelf 53 forming a valve seat and having a port which preferably is in the form of a narrow rectangular slot. A pipe 54 of flexible material communicates with this port and with the chamber of a diaphragm relay valve as will be hereinafter more fully described.

A valve 55 is slidably mounted upon the valve seat 53 and. is connected by a link 56 with the upper end of the lever arm ,42.

In the operation of the device the difl'erential movement of the lever arms 42 and 52, caused by unequal expansive movements of the wet and dry bulb thermostatic members, will actuate the valve 55 either to the open position illustrated in Fig. 5, or to closed position in which the port for the pipe 54 will be covered. This movement of the valve is utilized to govern pressure of the diaphragm motor of a relay valve which in turn governs the pressure of a diaphragm motor which actuates a valve for controlling the supply of moisture to the air of an enclosure.

In the construction illustrated air under pressure is supplied through a pipe 57 having a branch 58 provided with a restriction 59 through which air under pressure is supplied to the pipe 54 leading to the port of the valve seat 53. A branch 60 from the pipe 54 leads to the chamber of a diaphragm motor 61 of a relay valve.

The relay valve is illustrated in detail in Fig. 6 and comprises a body 62 having at its outer end a chamber 63 which is closed by a screw threaded plug 64. A relatively small bore 65 leads from the chamber 63 to'a chamber 66 in axial alinement therewith.

The ends of the bore 65. provide seats for a conical valve 67 the stem 68 of which engages the central portion of the diaphragm 69 of the motor and a helical spiral spring 7 0 surrounding the valve stem 68 norm-ally acts to maintain the valve in open position illustrated in Fig. 6. A small rod 71 is seated in and extends axially from the valve 67 through the bore 65 and at its opposite end engages a conical valve 72 which is normally held in seated position by a spring 73 in the chamber 63. The pipe 57 is provided with a branch 74 which leads to the chamber 63 and a port 75 leads from the bore 65 to a pipe 76 which in turn leads to the chamber of a diaphragm motor 77. The diaphragm 78 of this motor engages centrally the stem 79 of a valve (not shown) which controls the supply of air through a pipe 80 to an atomizer or series of atomizers 81 which are supplied with water from a pipe 82 in which the head of water is maintainedslightly below the level of the atomizer. Any suitable number of atomizing devices may be employed for an enclosure as is well known by the those skilled in the art.

. In the preliminary setting of the device the adjusting screw 39 is set to provide a predetermined wet bulb depression that is to say at a certain temperature difference between the wet anddry bulb thermostatic members asto cause the valve 55 to open the port in the valve seat 53 when a predetermined difference in temperature between the wet and dry bulb thermostatic elements is reached.

Air under pressure is supplied to the pipe 57 and passing through the restricted ports 59 of the branch 58 will build up a pressure in the pipe 54 if the valve 55 is in closed position. However, the instrument is usually set so that the valve 55 will not close the port leading to the pipe 54 when the humidity equals or exceeds the predetermined desired humidity.

In the operation of the device if the humidity of the enclosure exceeds a predetermined humidity and the temperature rises and falls without substantial change in the humidity, the lever arms 42 and 52 will be actuated in the same direction and with substantially equal movements and the valve will remain in open position. If, however, by reason of decrease of humidity the expansive movement of the wet bulb member, due to the more rapid evaporation of the moisture upon the surface thereof, exceeds that of the dry bulb member a differential movement of the leverarms 42 and 52 will be produced which will move the valve 55 to closed position, thereby preventing the escape of air from the pipe 54 and causing the pressure to be built up in said pipe and in the chamber of the diaphragm motor 61', so that the diaphragm 69 will force the valve 67 to closed position, thereby causing the rod 71 to open the valve 72 and permit air under pressure to pass from the pipe 57 through the pipe 74, the chamber 63, the bore 65 and passage 71 into the pipe 76 and to the chamber 77 of the main diaphragm motor. As the pressure builds up in the chamber of the diaphragm motor 77 the valve stem 78 will be actuated Cal When the predetermined degree of humidit has been attained the relative movement 0 the lever arms 52 and 42 will be such as again to move the valve 55 to open position, thereby relieving the pressure in the pipe 54 and permitting the springs -73 to restore the valves 67 and 72 to normal position,

thereby cutting off the supply of air through the pipe 74. The body 62 of the relay valve is provided with a port 83 leading to the chamber 66 so that when the valve 67 is restored to open position by the springs air is permitted to escape from the chamber of the diaphragm motor 7 7 through the pipe 76, the bore 65, chamber 66,, and exhaust port 83, thereby permitting the spring 7 9 again to close the valve in the compressed air pipe and discontinue the action of the moisturesupplying means.

Of course, regulators of this character are well known in the art andare used for regulatingvarious other types of moisture supplying mechanism.

Wet and dry bulb thermo-sensitive elements provided with the old form of corrugated diaphragms having a variable rate of expansion at different temperatures can be made to function properly to control humiditg only within limited wet bulb depression a justments. Where it is necessary that the instrument be adapted to control different percentages of .relative humidity only approximately accurate results can be secured as the ratio between the wet and dry bulb indications is not the same at the low temperature scale as at a high temperature scale.- This fact has long been recognized by those skilled in the art as involving an error inherent in vapor pressure instruments and various expedients have been resorted to to minimize this error, all of which have been costly and none strictly accurate. A change of one degree in either the wet or dry bulb temperature corresponds to a change of from three to four per cent in relative humidity; consequently, for close humidity regulation at high and low temperatures it is necessarythat the relative movements, caused by the relative expansion of the wet and dry bulb members, shall be accurately co-ordinated to secure the desired result and it is desirable that the instrument shall have a sensibility of at least one-fourth to one-half degree F. to maintain a desired redetermined substantially constant condition of humidity. This, which has been very difficult of accomplishment in instruments heretofore produced, is readily accomplished in instruments having thermosensitive elements embodying the present invention without the necessity of introducing corrective and adjusting mechanisms and the numerous disadvantages resulting therefrom.

It will, therefore, be obvious that by the present invention I have provided a thermosensitive element which can be manufactured more economically and with greater uniformity than similar element-s which have heretofore been produced; that such elements are capable of-"being embodied in thermostatic indicating and recording instruments with greater facility by reason of the elimination of the unequally graduated dials and the necessity for calibrating each instrument, and that such elements may be employd in regulating devices particularly those of the wet and dry bulb hygrometric type to produce movements of the mechanisms thereof with greater accuracy than has heretofore been accomplished and to provide means whereby the instrument will respond properly throughout the predetermined temperature range at any wet bulb setting.

It is to beunderstood that the particular embodiments of the invention disclosed herein are of an illustrative character and are not restrictive of the meaning and scope of the following claims.

Having thus described the invention, what is claimed as new, and desired to be secured by Letters Patent, is:

1. A thermo-sensitive cell with a confined volatile fluid having oppositely disposed like diaphragm walls of initially flat, thin sheet metal peripherally united to provide a rigid annulus, with the efiective areas of said walls circumscribed by said annulus, primarily distorted to slightly spherical form and expansible spherically within a predetermined temperature range by the vapor pressure of the fluid and producing uniform amounts of axial movement throughout saidtemperature range-corresponding with uniform changes in temperature by virtue of variations in the elastic resistance that is characteristic of said Walls and compensatory of the variation of the changes in vapor pressure that is characteristic of the confined fluid when subjected to uniform changes in temperature. I

2. A thermo-sensitive cell with a confined volatile fluid having oppositely disposed like diaphragm walls of initially flat, thin, sheet metal, peripherally united to provide a rigid annulus with the effective areas of said walls circumscribed by said annulus spherically distorted by the vapor pressure of the fluid expansible spherically within a predetermined temperature range and producing uniform amounts of axial movement throughout said temperature range'corresponding with uniform changes in temperature by virture of variation inthe elastic resistance that is characteristic of said Walls and compensatory of the variation of the changes in vapor pressure that is characteristic of the confined fluid when subjected to uniform changes in temperature.

having oppositely disposed initially flat diaphragm walls of thin sheet metal periphcrally united to provide a rigid annulus and confining a volatile fluid with the effective areas circumscribed by said annulus expansible spherically within a predetermined temperature range and producing uniform amounts of axial movement by elastic resistance com pensatory of the Varying changes in the vapor pressure of the confined fluid which result from uniform changes of temperature and means coupling the central portions of adjacent diaphragms in axial alinement. thereby to cause the resultant axial movement of said cells to be directly proportional to the variations in temperature to which said motor is subjected.

4. A regulator comprising thermostatic motors subject respectively to the wet and dry bulb temperatures ofthe air, each motor consisting of a plurality of thermo-se'nsitive cells having the same coefiicient of expansion and interchangeable with any other cell of the same or another motor of said regulator, each cell comprising initially flat diaphragm walls of thin sheet metal peripherally united to provide a rigid annulus with the effective areas of said walls circumscribed by said anconfining a volatile fluid and expansinulus, ble spherically within a predetermined temperature range, and producing uniform amounts of axial movement by elastic resistance compensatory of the varying changes in the vapor pressure of the confined fluid which result from uniform changes in temperature, and means detachably coupling the central portions of the contiguous diaphragms of A successive cells of each motor in axial alinement to provide a structure in which the combined axial-movement of the respective mo tors is directly proportional to variations in the temperature to which they are respectively subjected.

In testimony whereof, I have signed my name to this specification.

WILLIAM B. HODGE. 

